Several in vivo measurement systems are known in the art. They include swallowable electronic capsules which collect data and which transmit the data to a receiver system. These intestinal capsules, which are moved through the digestive system by the action of peristalsis, are used to measure pH (“Heidelberg” capsules), temperature (“CoreTemp” capsules) and pressure throughout the gastro-intestinal (GI) tract. They have also been used to measure gastric residence time, which is the time it takes for food to pass through the stomach and intestines. These intestinal capsules typically include a measuring system and a transmission system, where a transmitter transmits the measured data at radio frequencies to a receiver system.
U.S. Pat. No. 5,704,531, assigned to the State of Israel, Ministry of Defense, Armament Development Authority, and incorporated herein by reference, teaches an in vivo measurement system, in particular an in vivo camera system, which is carried by a swallowable capsule. In addition to the camera system there is an optical system for imaging an area of the GI tract onto the imager and a transmitter for transmitting the video output of the camera system. The overall system, including a capsule that can pass through the entire digestive tract, operates as an autonomous video endoscope. It also images the difficult to reach areas of the small intestine.
FIG. 1 shows a block diagram of the in vivo video camera system described in U.S. Pat. No. 5,704,531. The system captures and transmits images of the GI tract while passing through the gastro-intestinal lumen. The system contains a storage unit 100, a data processor 102, a camera 104, an image transmitter 106, an image receiver 108, which usually includes an antenna array, and an image monitor 110. Storage unit 100, data processor 102, image monitor 110, and image receiver 108 are located outside the patient's body. Camera 104, as it transits the GI tract, is in communication with image transmitter 106 located in capsule 112 and image receiver 108 located outside the body. Data processor 102 transfers frame data to and from storage unit 100 while analyzing the data. Processor 102 also transmits the analyzed data to image monitor 110 where a physician views it. The data can be viewed in real time or at some later date.
During a typical examination, the in vivo camera system may take anywhere from about four to eight hours or more to traverse the digestive tract. Assuming a capture rate of about 2 images per second, the total number of captured images can range from approximately 35,000 to 70,000 or more images. If these images were subsequently displayed as a video sequence at a rate of 30 frames per second, one would require 20-40 minutes of viewing time to observe the entire video. This estimate does not include the extra time needed to zoom in and/or decrease the frame rate for a more detailed examination of suspect areas.
In many situations, the physician may desire to navigate the video by jumping from one anatomical structure to another anatomical structure, rather than cueing and rewinding the video manually. This type of navigation is simplified when the video sequence is indexed according to anatomical structure. The indexing process entails establishing a set of key frames that are representative of certain anatomical structures of interest. Commonly assigned U.S. patent application Ser. No. 10/812,785, incorporated herein by reference, describes a method and system for identifying the anatomical structure corresponding to an in vivo image, based on the classification of image based and/or non-image based features of the in vivo image. The disclosure of patent application '785 reveals a rudimentary indexing system. For example, one may select the first in vivo images in the sequence as key frames that are classified according to each anatomical structure of interest. However, there remains a need in the art for indexing in vivo image sequences according to anatomical structure, in a way that is robust to the misclassification of individual in vivo images.